Re-powering my seacraft

[Bushwacker]

Originally Posted by RUSTYNTABATHA

. . . I thought the motors were rated at the prop in real world HP. 150 =150 at the prop shaft 175=175 at the prop shaft.. if and when i can swing the new motor i will be extatic with 4 + mpg @ 35 mph..

NAEBM rules only require that the actual HP be within +-10% of the advertised HP! BRP appears to be sandbagging by the full 10% on the ratings of their more mildly tuned motors, because they've published HP curves showing that the "150" E-TEC is actually 165 hp at the prop, so it's a very strong "150"! They also build the "175" and "200" hp motors on the same 158 cu. in. block, but I suspect the actual hp of the "175" is about 180-185, while the "200" maybe somewhere around 190-200. The 3.3L"200" HP big block V-6 is reportedly a very strong motor at about 220 hp, but it's also over 100 lbs heavier than the small block V-6.

If you look at HP/cu. in., that'll give you a clue as to how strong the motor really is, especially in the mid range where you want maximum torque for getting on plane. The more conservatively rated motors tend to have more mid-range torque than motors that are tuned for maximum top end HP. One of the most knowledgeable techs on the E-TEC Owners Forum claims that the 105 cu in. V-4 115 is actually has noticeably more mid-range torque than the 130 HP version of the same powerhead! HP and Torque are two different things, and both 2 and 4-stroke motors can be tuned to optimize one at the expense of the other!

[76Red18]

I'm still testing a new prop I purchaced for my 18. It's a Stiletto Bay Pro 3, 4 blade 14 1/4 x 15. I raised the motor all the way up (2" or so above the keel) but need to lower it a bit due to over heating at full throttle full trim. I hit 44 @ about 5500 rpm briefly before i had to back down on the throttle. Cruise was 32 @ 4000 rpm. The old Johnson 150 loves 4000 rpm. The boat was fully loaded. More testing this weekend.

[infanterene]

I tried a 3 blade 16P. I was able to hit 5500 +/- fully loaded but only went 45mph. My cruise dropped to 30-32mph and fuel consumption went up. It wouldnt plane as slow either.

Its weird but the 4B over propped setup felt better.

[McGillicuddy]

Originally Posted by infanterene

I tried a 3 blade 17P. I was able to hit 5500 +/- fully loaded but only went 45mph. My cruise dropped to 30-32mph and fuel consumption went up. It wouldnt plane as slow either.

Its weird but the 4B over propped setup felt better.

What 3 blade 17p prop did you try?

[Bushwacker]

4 Blades will always produce more stern lift than a 3B, so that's why you could stay on plane longer with the 4B. I think they generally have less slippage so they're more efficient at cruise, although the drag of the extra blade may cost you a few mph on top end.

Sounds like you just need to get your motor height corrected and then find the right combo of pitch/diameter 4B. You might try Ken at Prop Gods or try the PowerTech web site, where they have a data sheet you fill out with boat weight and the performance numbers you're getting with current prop. They will then advise what prop would best suit your application. If being able to hang on plane at low speed is a priority (which I think is important for a 20 that you run offshore), be sure to mention that.

[infanterene]

Originally Posted by McGillicuddy

What 3 blade 17p prop did you try?

It is a viper but I'm not 100% sure on the pitch. I tried it out again today. It was pretty rough in the bay so I didn't really pay attention to any numbers.

At one point I backed it down to about 20 mph and that's when I missed the 4 blade. It seems like my boat was dryer and handled rough conditions better with the 4b.

I think I'm going to just order a 4b x 15 and call it a day?

[Bushwacker]

On the BRP props, I think the Viper is a high speed prop that most of the dealers seem to be pushing, but for a 3B prop, the Rebel has a lot more blade area and acts somewhat like a 4B with lots of stern lift, sort of like the Merc Mirage. I tried a 15.25 X 17P Mirage 3+, but it wasn't as good as my 4B 14.125 x 20 Apollo, and I couldn't reach optimum rpm with either one at max load. My 15x15 4B PowerTech is a better heavy load prop than either of them. Would like to try a 15P Rebel, but it supposedly has very low slippage and acts like it has more pitch than advertised, so not sure I could turn it to optimum RPM.

[infanterene]

Originally Posted by Bushwacker

On the BRP props, I think the Viper is a high speed prop that most of the dealers seem to be pushing, but for a 3B prop, the Rebel has a lot more blade area and acts somewhat like a 4B with lots of stern lift, sort of like the Merc Mirage. I tried a 15.25 X 17P Mirage 3+, but it wasn't as good as my 4B 14.125 x 20 Apollo, and I couldn't reach optimum rpm with either one at max load. My 15x15 4B PowerTech is a better heavy load prop than either of them. Would like to try a 15P Rebel, but it supposedly has very low slippage and acts like it has more pitch than advertised, so not sure I could turn it to optimum RPM.

I dont understand how you can turn a 4B 14.125 x 20 and I cant turn 4B 14.5 x 17?

[deadrise]

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